﻿186 BRITISH FOSSIL CEPHALOPODA. 



Relations. — There is a group of small ribbed Cyrtocerata, figured by Barrande, 

 to which this species belongs, amongst which C. urbanum (' Syst. Silur. de Boheme,' 

 vol. ii. pi. 198, figs. 11-20) alone agrees with it in having the ribs rising to the 

 convex side ; but they are of equal size throughout, and there is a septum between 

 each. 



Distribution. — In the Bala Beds, Bala (1). 



Cyrtoceras {Piloceras) inraginatum, Salter. 



See Salter, 'Quart. Journ. Geol. Soc' vol. xiv. pi. 13, figs. 17-21, p. 376. 



I have little to add to the remarks on the Piloceras as a genus, in which I throw 

 doubt on its being a Cephalopod at all. I have been to Durness to see if it were 

 possible to find any septa passing beyond the fossil in the matrix, but without success ; 

 neither the collectors there, nor Mr. Peach, their original discoverer, ever saw septa 

 extending beyond them, and there are no signs of any such in the numerous speci- 

 mens in the Museum of Practical Geology, of the Royal College of Science, Dublin, 

 or elsewhere. The surface, however, is probably worn away in all the specimens ; 

 and the rings figured by Salter, and considered by him as ornaments, but by 

 Barrande as the junction of septa to the siphuncle, may be due only to weathering. 

 The sheaths are parallel to each other and to the exterior, which is one of them, 

 so that the manner in which the inner ones are supported has not been made out. 

 I doubt if there ever was an interval between them not filled by any organically 

 formed material, for had there been they must have floated loosely one inside the 

 other. The organism, whatever it is, must wait elucidation by materials not yet 

 extracted from the rocks. 



GrROUP II. InFLATI. 



Genus Poterioceras. 



POTERIOCERAS (?) APPROXIMATUM, M'Coy, PI. XXIY. fig. 6. 



1846. Poterioceras approximatum, M'Coy, ' Silurian Fossils of Ireland,' pi. 1, fig. 5, p. 10. 

 Syn. 1843. Gomphoceras subfusiforme, Portlock, ' Geological Eeport,' pi. 24, fig. 5. 



Type. — The section is now elliptic, perhaps by compression. The curvature is 

 uniform on both sides; the general radius of curvature being 16 lines. The rate of 

 increase on the septate portion is 1 in 4 ; the greatest diameter being opposite the 

 last chamber, and the body-chamber decreasing again with the same curve. No 

 aperture is seen. The septa are about y L the long diameter apart, and the sutures 

 are nearly direct. Greatest length, 14 lines ; greatest diameter, 9 lines. From Lower 

 Silurian Sandstone at Pomeroy. In the Museum of the Royal Dublin Society. 





